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Chapter 4
The Chemical Basis of Life
Matter
Matter = any material
substance with Mass
& Volume
Matter
comes in 3 phases
Solid
Gas
Liquid
Solid
Definite Shape
Definite Volume
Liquid
Indefinite Shape – takes the
shape of the container
Definite Volume
Gas
Indefinite Shape – takes the
shape of the container
Indefinite Volume – can
expand and be compressed
Elements
Pure substance that can not be broken down into other
substances by chemical means
Examples of Elements
C = Carbon
Na = Sodium
O = Oxygen
Ca = Calcium
H = Hydrogen
K = Potassium
N = Nitrogen
I = Iodine
Cl = Chlorine
S = Sulfur
P = Phosphorus
• 4 elements make up 96% of all living matter
– Hydrogen (H)
– Oxygen (O)
– Nitrogen (N)
– Carbon (C)
• Most of remaining 4%
is made of:
–
–
–
–
Calcium (Ca),
phosphorus (P),
potassium (K),
sulfur (S)
• Trace elements Make
up less than 0.01 % of
body mass
– Essential to life
Atom the smallest particle making up elements
Sub-atomic Particles
Protons p+ - positive charge,
in nucleus
Neutrons n0 – no charge,
in nucleus
Electrons - e- negative charge,
orbiting nucleus
Carbon Atom
6
C
12.011
Atomic # = # of p+ and # of eCarbon has 6 p+ and 6 e-
Atomic Mass minus Atomic # = # of n0
Carbon has 6 n0
HELIUM ATOM
Shell
proton
+
-
N
N
+
electron
What do these particles consist of?
-
neutron
Bohr Diagram and Lewis
Structure
ATOMIC STRUCTURE
Electrons are arranged in Energy Levels or Shells
around the nucleus of an atom.
•
first shell
a maximum of 2 electrons
•
second shell
a maximum of 8 electrons
•
third shell
a maximum of 8 electrons
Bigger energy level = higher energy
ATOMIC STRUCTURE: Bohr Diagram
With the Bohr Diagram (Dot & Cross diagrams) elements
and compounds are represented by Dots or Crosses to show
electrons, and circles to show the shells. For example;
X
Nitrogen
X
X 7P+
7n0
XX
X
X
N
7
14
Bohr Diagrams
Draw the Bohr Diagram for the following elements:
a)
O
8
b)
16
Cl
X
17
35
X
X X
XX
X
X
8p+
8n0
X
X X
X
X
X
X
17p+
X 18n0 X
X X
X X
X
X
X
X
Bohr Diagrams
Draw the Bohr Diagram for the following elements:
c)
B
5
11
d)
10
Ne 20
X X
X X
X
X
5p+
6n0
X
X
X
10p+
X 10n0 X
X X
X
X
Valence Electrons
• The electrons on the outermost
energy level
• These electrons determine the
element’s chemical properties
and its ability to form chemical
bonds.
Lewis Structure of Atom
• The chemical symbol for the atom is surrounded
by a number of dots corresponding to the number
of valence electrons.
• Examples
– Hydrogen atom has 1 valence electron
– Fluorine atom has 7 valence electrons
H
F
Lewis Structure
• Draw the Lewis Structure for the following elements:
a)
Li
b)
c)
P
d)
Cl
Mg
Chemical Bonding
Ionic and Covalent
Chemical Bonds
• Atoms react with one another to fill their
outer energy levels
• Transferring or sharing electrons creates
an attraction (chemical bond) that holds
atoms together
Noble Gases
• Helium, neon and argon are atoms which do not react
with other atoms.
• We call them “Noble Gases” because of this.
• Each of these gases has a full outer electron shell.
2p2n
He
2
4
10p10n
Ne 10
20
2,8
18p22n
18
Ar 40
2,8,8
IONIC BONDS
• Ionic bond: one atom transfers an
electron to another atom
• Oppositely charged ions are attracted
to one another forming a chemical bond
 an ionic bond
Sodium
11
Na 23
e.c. 2,8,1
11p
12n
11 protons
12 neutrons
11 electrons
Chlorine
17
Cl 35
e.c. 2,8,7
17p
18n
17 protons
18 Neutrons
17 electrons
The Sodium atom has 1
Electron in it’s outer shell.
Na
e.c. 2,8,1
Atom
The Sodium loses 1 electron
to leave a complete outer
shell.
It is now a Sodium ion with a
charge of 1 +
(Na +)
e.c. (2,8)+
Ion
+
The Chlorine atom has 7
electrons in it’s outer shell.
Cl
e.c. 2,8,7
Atom
The Chlorine gains 1 electron
to gain a complete outer
shell.
It is now a Chlorine ion with a
charge of 1 -
(Cl - )
e.c. (2,8,8)Ion
The Ionic Bond
Chlorine
atom
Sodium atom
Na
Cl
Sodium ion
+
(Na +)
-
Chlorine ion
(Cl -)
• The sodium atom loses one electron to attain a complete outer shell and become
a positive ion (Na +).
• The Chlorine atom gains one electron to attain a complete outer shell and
become a negative ion (Cl –).
• Strong forces attract the sodium and chlorine ions.
Covalent Bond
• Formed when atoms share electrons
• Electrons may be shared equally or
unequally
• Molecule: two or more atoms held
together by covalent bonds
Chlorine atom 2,8,7
2 Chlorine atoms
Outer shells only
Chlorine molecule Cl2
Electrons shared
Each outer shell has 8 electrons
Forces (bonds) between atoms in the molecule are very strong
Molecules have no overall electric charge
Covalent bonds can be represented in 3 ways:
Chlorine Cl2
Cl
Cl
Cl
Cl
Cl
Cl
16
Oxygen O 8
Oxygen atom 2,6
2 Oxygen atoms (outer shells only)
Double covalent bond
O
O